The present invention relates to mounting piezoelectric devices. More particularly the present invention relates to mounting a piezoelectric transformer to a printed circuit board with a coil spring in order to increase mechanical compliance.
The miniaturization of circuits and components remains a top priority in most electronic industries. The miniaturization of solid-state components and combination-type circuitry chips, such as central processor units, digital signal processors, memory, etc., has been so successful that the packaging and electrical connections for access to such small devices has become one of the major roadblocks for further miniaturization. One of the packaging problems for some types of miniaturization circuits, such as for piezoelectric devices, is how to both support the piezoelectric device and make electrical connections without adversely affecting the operation and performance.
A piezoelectric transformer transfers energy through acoustic vibration. At the resonance frequency of the piezoelectric transformer a vibrational standing wave exists in the device which defines nodes and anti-nodes of the standing wave. Efficient piezoelectric transformers resonate with a very high mechanical Q. Any mechanical dampening of the vibration of the piezoelectric transformer reduces the Q and decreases the efficiency of the transformer. Practical application of the piezoelectric transformer normally requires that the device be attached to a printed circuit board and that three or four electrical connections be made to the printed circuit board. Therefore, it is necessary to mount the piezoelectric transformer in a manner that minimizes mechanical stress on the piezoelectric transformer in order to maximize efficiency.
Prior art mounting techniques often included the use of silicon-type adhesives or double-sided tapes for mounting the piezoelectric device to a printed circuit board. Such techniques offer some stability against g-forces, rotational and torsional forces, but dampen the vibrational force of the piezoelectric transformer. In many instances these prior art mounting techniques are unacceptable because the mechanical and electrical attachments of the piezoelectric transformer to the printed circuit board become fractured as a result of the fact that vibrational stresses are concentrated at these portions. Additionally, these prior art mounting methods reduce the efficiency of the piezoelectric transformer by 3-5%.
Therefore, it would be advantageous to provide a simple and inexpensive method for flexibly mounting a piezoelectric device on a printed circuit board in order to minimize mechanical dampening of the vibration of the piezoelectric device.
The present invention solves the problem of the prior art by providing controlled mechanical compliance in all directions. The compliance may be adjusted by varying the spring height, material, coil and wire diameter and coil spacing. Springs with approximately the same coil diameter as the transformer pads can be attached to the piezoelectric transformer.
The present invention provides a method of mounting a piezoelectric device having a plurality of mounting pads directly to a printed circuit board comprising the steps of providing a piezoelectric device, miniature conductive springs and a printed circuit board, attaching the springs to mounting pads of the piezoelectric transformer, and attaching the springs to the printed circuit board. Also disclosed is an apparatus made according to the method.